Priority is claimed from Korean Patent Application No. 10-2004-0090890, filed on Nov. 9, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical scanner capable of flip chip hermetic packaging, and more particularly, to an optical scanner capable of hermetic sealing with a round of flip-chip bonding.
2. Description of the Related Art
Micro-electromechanical system (MEMS) optical scanners employed in projection televisions and the like deflect a laser beam using an electrostatic effect produced by comb-typed electrodes. Such micro-optical scanners are generally structured such that a mirror is suspended to seesaw by a supporter formed on a substrate such as a silicon-on insulator (SOI) wafer. A plurality of movable comb electrodes are vertically formed at both sides of the mirror, and a plurality of static comb electrodes are vertically installed on the SOI wafer to alternate with the movable comb electrodes. In recent years, optical scanners with a double comb electrode structure in which static comb electrodes are installed over and under movable comb electrodes have been developed. In this structure, voltages having opposite polarities are applied to the movable comb electrodes and the static comb electrodes, and an electrostatic force is generated between the movable and static electrodes, causing the mirror to seesaw at high speed. Accordingly, a laser beam incident on the mirror can be deflected at high speed.
Such optical scanners are very sensitive to environmental conditions since the mirror has a very small size (e.g., a size less than several millimeters). Accordingly, hermetic sealing is needed to maintain the performance of the optical scanners and protect the optical scanners from changes in environmental conditions.
FIGS. 1A through 1E are cross-sectional views illustrating a process of hermetically sealing an optical scanner.
First, FIG. 1A is a cross-sectional view illustrating lower and upper structures of an optical scanner with a double comb electrode structure. In the lower structure, a mirror 12 is suspended over a lower substrate 10 through a torsion spring 13, and movable comb electrodes 14a and 14b are formed at both sides of the mirror 12. Lower static comb electrodes 11a and 11b are installed on the lower substrate 10 under the movable comb electrodes 14a and 14b. The lower static comb electrodes 11a and 11b receive voltage through first lower support parts 16, and electrode pads 18 are formed under the first lower support parts 16. The movable comb electrodes 14a and 14b receive voltage through second lower support parts 17 over the first lower support parts 16. Although not shown, the second lower support parts 17 extend up to the torsion spring 13 to support the torsion spring 13. An insulation layer 19 is interposed between the first lower support parts 16 and the second lower support parts 17.
In the upper structure, upper static comb electrodes 21a and 21b are installed on an upper substrate 20 to face the lower static comb electrodes 11a and 11b. The upper static comb electrodes 21a and 21b receive voltage through upper support parts 24. To apply voltage to the upper support parts 24, a plurality of through-holes 22 are formed on the upper substrate 20. Electrode pads 23 are formed along the through-holes 22 and a top surface of the upper substrate 20. Furthermore, solder layers 25 are formed on the upper support parts 24 to bond the upper substrate to the lower substrate 10. Although not shown, an opening through which a laser beam can pass is formed on a portion of the upper substrate 20 to face the mirror 12.
The separately manufactured lower structure 10 and upper structure 20 are assembled through a flip-chip bonding process as shown in FIG. 1B. That is, the solder layers 25 of the upper substrate 20 are bonded to metal pads 15 on the second lower support parts 17 of the lower substrate 10, thereby completing an optical scanner.
The completed scanner is mounted on a bottom surface of a ceramic package 30 using a die bonding method or the like as shown in FIG. 1C. After the optical scanner is mounted on the bottom surface of the ceramic package 30, wires 37 are connected between the electrode pads 18 and 23 and electrode pads (not shown) disposed on inner walls of the ceramic package 30 as shown in FIG. 1D. The electrode pads of the ceramic package 30 are connected to leads 36 that downwardly protrude from the ceramic package 30, and receive voltage from the outside. After the wiring is completed, a glass 38 is bonded to top surfaces of side walls 31 of the ceramic package 30, as shown in FIG. 1E, to completely seal the optical scanner from the outside. Although the side walls 31 are shown at both sides of the ceramic package 30 in FIGS. 1C through 1E, the side walls 31 are also formed at front and rear sides of the ceramic package 30, making it possible to completely seal the optical scanner.
As described above, a conventional method of manufacturing an optical scanner includes a process of bonding upper and lower structures of the optical scanner, a process of die-bonding the optical scanner to a ceramic package, a process of connecting wires between the ceramic package and the optical scanner, and a process of hermetically sealing the optical scanner from the outside by mounting a glass on side walls of the ceramic package. Accordingly, manufacturing processes are complex and much manufacturing time and costs are required. Moreover, since the ceramic package surrounding the optical scanner is three or four times larger than a real optical scanner, the ceramic package runs counter to a recent trend of a small layer display. When the ceramic package is used to manufacture a laser display, there is a limitation in miniaturization. In addition, since bonding is performed many times and many kinds of solders are used in each process, the reliability of the laser display is affected, and since the number of processes is high, the yield of the laser display is reduced.